Zipfian

Zipfian distribution implementation.

Installation

Add this line to your application's Gemfile:

gem 'zipfian'

And then execute:

$ bundle

Or install it yourself as:

$ gem install zipfian

Usage

# 1000: Number of elements
#  1.0: Exponent
z = Zipfian.new 1000, 1.0

puts z.n    # 1000
puts z.s    # 1.0

(1..1000).each do |i|
  puts [z.pmf(i), z.cdf(i)].join ' - '
end

puts z.sample    # Integer between 1 and 1000

Initialization overhead (CPU, Memory)

On initialization, each Zipfian instance precalculates the values of cumulative distribution function for every integer point in the range and stores them in memory. Thus, as the range gets larger, initialization will take longer, and each instance will take up more memory space accordingly.

Caching

To avoid repeated overhead when multiple Zipfian instances are used, you can optionally enable thread-safe caching of precalculated data at class-level by setting the third parameter of the constructor to true.

# Cache precalculated data
z1 = Zipfian.new 1000000, 0.5, true

# Returns immediately. No more memory consumption
z2 = Zipfian.new 1000000, 0.5

A workaround of memory limitation

If the range is exceptionally large, it wouldn't be just possible to hold all the calculated values in memory. In such cases, you may need to approximate the distibution with a smaller Zipfian distribution.

z = Zipfian.new 1000000, 0.5

puts z.sample * 1000 - rand(1000)

Contributing

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Added some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request